Hydraulic systems for adjusting hospital beds, for example adjusting of the supporting surface of a hospital bed in which, for example, a mattress is situated on which a patient can lie down, are generally known. For example, in U.S. Pat. No. 4,959,957 a hydraulic unit for adjusting the height of a hospital bed is illustrated. The unit: comprises a single-acting hydraulic actuator and a hydraulic plunger pump. The actuator is coupled to a height-adjustable subframe via a system of rods. The pump is operated by means of a foot-operated lever. The known hydraulic system is furthermore provided with a relief valve which can be operated separately and which relieves the actuator when it is operated, so that the subframe can be lowered.
Another hospital bed with an associated hydraulic system is known from EP 0 341 358 A1. Compared to the system from U.S. Pat. No. 4,959,957, this system comprises a number of additional actuators, each of which is designed to adjust an associated adjustable section of the supporting surface. This known hospital bed has a supporting surface with adjustable back and leg sections, as is very common in practice. The hydraulic system is provided with a hand-operable valve assembly operating member which is designed in such a manner that, by being operated, it selects a specific actuator and connects the latter to the pump in order to thus adjust a specific section of the supporting surface or to set the height of the subframe. The hydraulic system known from EP 0 341 358 A1 is furthermore provided with a pump activating member in the form of a foot-operable lever which is connected to the pump. The purpose of this pump activating member is to actuate the pump so that an actuator which is selected by means of the valve assembly operating member is fed with pressurized hydraulic liquid. In addition, the known hydraulic system is provided with a further, i.e. a third, member which can be operated by an operator and which is connected to a separate relief valve. By operating this third operating member, an operator can produce a connection between a selected actuator and the reservoir and thus a return movement can be carried out.
In order to operate the hydraulic system known from EP 0 341 358 A1, the operator needs at least one of his/her hands to operate the valve assembly operating member. This means that the operator is not able to use both his/her hands (if any) for treating a patient when the operator operates the valve assembly operating member. In many cases, the procedures which have to be carried out on a patient require the use of both hands by the person carrying out the procedure, which is not possible in the case of the hydraulic system known from EP 0 341 358 A1. This may lead to a reduction in care for the patient, require additional care personnel or delay the operation of the hydraulic system (which is undesirable in, for example, hospitals).
The German Utility Model DE 298 15 699 U1 discloses an operating table with hydraulic adjustable members on the supporting surface. The hydraulic system of the operating table from DE 298 15 699 U1 comprises a first lever which can be displaced in a horizontal plane by means of which a hydraulic actuator which is associated with one of the adjustable members can be selected. This lever can be moved into unique positions in order thus to select a specific hydraulic actuator. Like the hydraulic system known from EP 0 341 358 A1, the hydraulic system from DE 298 15 699 U1 comprises a pump activating member in the form of a second foot-operable lever which is connected to the hydraulic pump. In addition, the hydraulic system comprises a third lever which can be foot-operated by an operator and is connected to a separate relief valve. By operating the third lever, the operator can produce a connection between a selected actuator and the reservoir and thus a return movement can be carried out.
A further drawback of both EP 0 341 358 A1 and DE 298 15 699 U1 is that the positioning of the members that can be operated, in particular the foot-operated levers for actuating and relieving the hydraulic actuators, is not satisfactory from an ergonomic point of view. With both the hydraulic system from EP 0 341 358 A1 and DE 298 15 699 U1, said foot-operated levers are arranged in close proximity to one another. This may result in mistakes being made regarding which lever is to be operated by the operator, which may have highly undesirable consequences in the case of a hospital bed.